Snow set to blanket Washington region this weekend: Forecast amounts and storm timeline

A winter weather advisory is in effect around the Beltway

10:05 p.m. - Increasing the snow forecast

The trend of the day has continued with the afternoon and evening weather models. In short, more snow is now expected compared to earlier.

(Capital Weather Gang) ((Capital Weather Gang))

As such, we've decided to bump up numbers about an inch on all ends. Three to six inches is now the most likely scenario in the immediate area, with higher totals of four to seven inches anticipated across our southern suburbs.

Snow is still on track to arrive tomorrow afternoon. It it shouldn’t take long to stick given cold temperatures going in, and the bulk of the accumulation occurs overnight. Some then persists in a tapering fashion into Sunday.

3:45 p.m. - Latest models trending slightly snowier

The latest simulations from the NAM model (both its low and high resolution versions), just in, suggest our most likely forecast of 2 to 4 inches for D.C. may be too low. They suggest 5 to 7 inches (and a little more south of Washington and a little less to the north). If models coming in later this afternoon and evening support these higher numbers, we may bump up ours as well. Stay tuned for any forecast updates this evening and early Saturday.

2:30 p.m. - Winter weather advisory and winter storm warnings issued

The National Weather Service has issued a winter weather advisory for the immediate Washington, D.C. area, and points north from 4 p.m. Saturday to 7 a.m. Sunday. It calls for 3 to 5 inches of snow that will cause “slippery road conditions.”

South of Fairfax, Loudoun and Prince George’s counties, it has issued a winter storm warning from 4 p.m. Saturday to 1 p.m. on Sunday. In this zone, which includes Fauquier and Prince William counties, as well as southern Maryland, it predicts 3 to 7 inches of snow. Travel in this area could be “very hazardous,” it cautions.

The Weather Service’s forecast is generally in line with our expectations for the region, described in detail below.

Original post from midday

Forecast models have come into reasonably good agreement that the Washington region will witness a light to moderate snowfall this weekend. The snow should begin Saturday afternoon and taper off during the day Sunday.

Two to four inches of accumulation is most likely inside the Beltway. Washington’s southern suburbs through central Virginia should see the heaviest snowfall, with amounts of three to six inches most common. Somewhat lighter amounts of about one to three inches are predicted in our northern areas.

Once the snow begins Saturday afternoon, temperatures will fall below freezing, and it should shortly thereafter begin to stick. Especially by Saturday evening, when the snow may pick up a bit, roads may turn slick. Through at least Sunday morning, travel may be challenging.

“This looks like one of those storms with a drawn-out period of light snow that could last well into Sunday, with the snowfall intensity occasionally picking up,” said Wes Junker, Capital Weather Gang’s winter-weather expert. “The heaviest snowfall will probably fall Saturday evening around Washington and very early Sunday morning in our southern areas.”

As with most snow events in the Washington region, slight shifts in the storm track could result in more or less snow than predicted. If the storm jogs a bit farther north Sunday, heavier snow than predicted could fall from Washington to Baltimore and points north, and the snow could last longer into Sunday afternoon. But if dry air suppresses the storm to the south, accumulations will be limited, and the snow could end as early as Sunday morning.

Storm timeline

10 a.m. to 4 p.m. Saturday: Flurries and light snow begins from southwest to northeast. Little accumulation except maybe a coating or so in our west and southwest areas. Temperatures 30 to 35 degrees, falling to 28 to 32 once snow becomes steady.

4 p.m. Saturday to midnight Sunday: Light to moderate snow. Accumulation of a coating to two inches or so possible, with the heaviest west and northwest of Washington. Temperatures 27 to 31.

Midnight to 8 a.m. Sunday: Light to moderate snow. Snow decreasing in northwest areas but increasing in our southern areas. Accumulation of one to three inches or so possible, heaviest south of Washington. Temperatures 26 to 30.

8 a.m. to noon Sunday: Light to moderate snow. Snow may begin to taper off in our northern areas between midmorning and noon. Accumulations of a coating to an inch or so possible, heaviest south of Washington. Temperatures 28 to 32.

Noon to 5 p.m. Sunday: Snow tapers off by early afternoon or so from the District north and by late afternoon in our southern areas. Little additional accumulation, except for a coating or so in southern areas. Temperatures 30 to 34.

American (GFS) model storm forecast.

Storm impact

On our one-to-five winter storm impact scale, we rate this storm a Category 2, or disruptive, event for the entire region, one step up from a nuisance storm (Category 1) and one step down from a significant winter storm (Category 3).

Category 2 storms produce slick roads and some flight delays (but not widespread cancellations) and often lead to school closings and delays. But because this storm is happening over a weekend and leading into a Sunday morning (when many schools and businesses are closed), the impact is reduced.

(TWP)

Still, the snow may disrupt church services and Sunday schools across the region. It’s also possible that the effects of the storm linger into Monday, leading to some school closings and delays. That said, most of the accumulating snow should be over by midday Sunday except perhaps in our far southern areas. This should allow crews time to clear roads ahead of the Monday morning commute. We plan to post a SchoolCast and FedCast late Sunday afternoon with projections for Monday morning.

(Note that we consider this a low-end Category 2 event in our northern areas but a high-end Category 2 in our southern areas, not far off from a Category 3.)

Model forecasts

Our confidence in the overall forecast has increased somewhat since Thursday because model predictions have come into better agreement. However, as you can see below, there are still differences — hence why our confidence in our own snowfall forecast is just moderate.

Predictions from other forecasting outlets

Meteorologists from the National Weather Service and other news organizations generally agree that about one to three or two to four inches of snow is most likely for the immediate area. Here are the snowfall prediction maps we could find for comparison.

Jason SamenowJason Samenow is The Washington Post’s weather editor and Capital Weather Gang's chief meteorologist. He earned a master's degree in atmospheric science and spent 10 years as a climate change science analyst for the U.S. government. He holds the Digital Seal of Approval from the National Weather Association. Follow